Computed tomography (CT) systems and methods are widely used, particularly for medical imaging and diagnosis. CT systems generally create projection images through a subject's body at a series of projection angles. A radiation source, such as an X-ray tube, irradiates the body from one side. Images of the subject's body can be reconstructed from the projection data (i.e., the projection images acquired at various projection angles), using various reconstruction techniques such as filtered back-projection, iterative reconstruction, etc.
Many clinical applications can benefit from spectral CT technology, which can provide improvement in material differentiation and beam-hardening correction. Spectral CT data can be obtained using one of several technologies, including: direct X-ray detection using semiconductor-based photon-counting detectors, dual-source systems to perform dual-energy scans, kVp-switching systems to perform dual-energy scans, performing sequential scans at different X-ray energies, and using layered detectors capable of simultaneously measuring multiple energies to simultaneously realize a dual-energy scan. When a spectral CT system uses energy scans performed at different times, motion of the patient in between scans can introduce errors and artifacts into the material decomposition.